Filter units are widely used for separating particulate material from a slurry in which it is contained. For example, manufacturing process fluids such as "cutting-coolant-fluid" used in metal machining operations, such as in an automotive engine manufacturing plant, are usually circulated in a system serving a number of manufacturing machines. In such systems a filter device removes undesired particulate, viz., metal particles or the like, which enter the fluid as it moves through its normal path in the manufacturing process between passes through the filter device. The continuous recirculation of the coolant draws air from the environment into the coolant where the trapped air becomes saturated with moisture and then escapes to the plant atmosphere, while contaminants in the air, such as lint, pollen, micro organisms and dust are deposited and trapped in the coolant. In addition, lubricating oils from the machinery and spent oils from the manufacturing process are continually absorbed and trapped in the coolant as well.
The filter capacity must be suitable to meet the needs of the machining operation involved. The filter device is usually selected on the basis of the volume of cutting-coolant needed and the competitive prices of devices considered for use compared to the planned expenditure. Current technology uses either high flow rate permanent filter media, or high flow rate disposable filter media, or a combination of both. Regardless of which method is used, the particles which do not pass through the filter media collect on top of the media as an increasingly thicker "filter cake", which in turn removes progressively smaller particles which would have continued to pass through but for the build-up of filter cake. As the filter cake builds, it becomes progressively tighter with the result that the flow through the system becomes progressively choked by continued accumulation of fine particles in the filter cake to the point where the flow is restricted to a point of capacity failure. At such point, the filter cake must be removed and the filter restarted. Following restarting of the filter, the continuous accumulation of dirt particles in the slurry as filter cake building continues, results in the build-up of residual fines and chemical compounds in the cutting-coolant-fluid adversely effecting the quality of the fluid. When the quality of the coolant reaches sub-acceptable levels, the coolant is dumped from the system and the system is then cleaned and recharged with the result that the dumping and cleaning operations become a major cause for increase in the size of waste treatment plants utilized in the respective manufacturing plants of which they are a part.
As civilization progresses, the need for pure water and recycling becomes more and more intense. Current technology uses settling systems which consist of farms of huge settling tanks, some of which are indoors, requiring capital expenditures which can only be written off over periods of many years. To enhance the operation of settling systems, chemical additives are used, and, their use in turn increases the bulk of the waste discharge and adds to the pollution load. With increasing bulk discharge, sophisticated de-watering devices are used to then decrease the bulk of the waste and allow it to be used as landfill.
Sophisticated manufacturing processes demand more and more pure water to accomplish their goals. We can no longer use the classic solution of dilution to solve the pollution problem. We must deal with pollution at the source, which means that recycling is not only the practical solution to the pollution problem, it is the only solution for the survival of our planet. The key to the eventual control of water and air pollution in combination with modern membrane technology demands a complete rethinking of the methods used to remove particulate matter from air and water.
Recycling of coolants was first recognized in the manufacturing industry in the early 1940's. In a metal machining operation such as mentioned above, a "cutting-coolant-fluid" requirement could be of the order of 5000 gallons per minute.
Filter devices using filter cake formed of either the dirt to be removed or artificial filter aids, viz., diatomaceous earth, to produce a filter cake, still represents the state of the art accepted by industry. The result is inefficiency, pollution and waste. Regardless of the method used, the flow rate through the filter area is the critical factor. Modern filter devices use flow rates of five and ten gallons per minute per square foot of filter area, and in roughing operations, even thirty gallons per minute per square foot. These flow parameters are justified because the cost of filter area for an operating system is of the order of $1,000.00/sq. ft. of filter area for a system requiring as much as 100 sq. ft. of filter area, while smaller systems can be even $2,000.00/sq. ft. In addition, even if the cost could be justified to double the filter area, using modern technology the floor space required for the equipment would be impractical.
An object of this invention is to provide a filter device that (1) economically allows the use of amounts of filter area that are massive in comparison to current practices described above and at the same time permits the use in a compact space, (2) provides the amount of filter area necessary for a low rate to avoid filter cake buildup, (3) provides the amount of filter area necessary for a flow rate that does not mechanically hold contaminants to the filter area against gravity forces, (4) provides the amount of filter area necessary to allow osmosis-like flow through substantially permanent membranes using low pressure and negligible fluid velocity, (5) may be continuously operated, (6) provides a substantially permanent filter media or membrane, (7) has a throughput at substantially constant volume, (8) may have a filter membrane which maintains constant particle size discrimination so particulate of acceptable and smaller sizes passes through the membrane, and (9) in which the particulate material which does not pass through the membrane tends to fall out of the slurry to concentrate such particulate in a location from which it may be removed from the filter device while the filter device remains in operation.
A further object of this invention is to provide a filter device in which filter areas are arranged in a vertical attitude and immersed in a slurry in a slurry holding vessel.
A further object of this invention is to provide in such a filter device massive amounts of substantially permanent filter area that is integrated into the slurry holding vessel so as to divide the slurry holding vessel to hold unfiltered slurry on one side of the filter area and clean, filtered slurry on the opposite side of the filter area in the same holding vessel.
A further object of this invention is to provide a filter device that uses a substantially permanent membrane to attain the degree of constant discrimination filtration desired at a constant flow without the necessity of building a filter cake.
A further object of this invention is to provide a filter device of the above mentioned character in which particles with a density greater than the density of the slurry fluid can agglomerate and settle to the bottom of the vessel for removal.
A further object of this invention is to provide a filter device of the above mentioned character in which floatable particles and oils of the slurry are not held against the filter surface, but rather rise to the top of the slurry in the vessel for removal by skimming.
Another object of this invention is to provide for such a filter screen assembly, a filter screen unit which is of simple construction, die moldable, durable, strong, inexpensive, easy to assemble, clean and replace, and which resists degradation under the conditions and substances present in the environment it is subjected to in the operation of the filter screen.
Another object of this invention is to provide a slurry filter screen unit having oppositely faced parallel filter faces, each having spacing support means projecting toward the other so that inward forces applied to one filter face are mechanically transferred to the opposite face to substantially offset forces directed inwardly against the latter.
Another object of this invention is to provide such a filter screen unit with a filter media web overlying the filter faces and adapted to filter from the slurry passing through the media all particles larger than a predetermined size which would otherwise pass through the filter faces of the unit.
A further object of this invention is to provide a filter screen assembly having filter media of bag-like form overlying the filter faces of the unit.
A further object of this invention is to provide a filter chip substantially enveloped by media screen assembly having substantial area and the capability of discrete selection of particle size to be passed through while having a relatively small sealing surface cooperating with a portion of the chip extending outward from the enveloping media.